1. Field of the Invention
The invention relates to an apparatus for sealing rotary tubes, and more particularly, to a seal that is suitable for the sealing of rotary tube drum devices, such as those used in furnaces for combustion, thermolysis, pyrolysis and similar processes.
2. Description of the Related Art
Seals are needed to achieve gas-impermeable separation between the various joined components of a furnace. For example, a gas-impermeable seal is required between a rotating tube drum and the stationary inlet and discharge housing to which the drum connects. These seals must be suitable for operation at temperatures above 750 degrees (Fahrenheit) and resistive to deformation--which tends to make the seals ineffective. The seals must also be able to withstand attacks by abrasive gases, abrasive solid particles and resinous oils and tars, and the wear associated therewith. Furthermore, the seals must be capable of sustained operation with little maintenance.
According to the prior art, rotary drums commonly use resilient elements such as, for example, gasket strips, placed into slots or other seals to achieve gas-impermeability between the various components. However, gasket strips are subject to clogging with resinous products that can lead to the ultimate failure of such seals. Moreover, seals of this type can become baked onto the sealing surfaces, i.e. onto the joints between the rotary tubes, in which event their impermeability is no longer ensured. In addition, maintenance and replacement of gasket-type seals can be expensive.
German Patent Number DE 43 31 556 A1 discloses a sliding ring seal for sealing a hot tube against a housing. The ring seal is attached to the tube by a nozzle having a central opening. The nozzle serves to lower the temperature of the sliding ring seal or alternatively, at the sealing point. A lubrication system is required to move the ring seal from the nozzle to its mounting location between the hot tube and the housing. In addition to this disadvantage, this solution requires large structural volume, and heating of the sealing points cannot be completely prevented. This creates the danger that the ring seals, which usually are large, will warp from the heat and that leaks will eventually develop, as is generally the case with linear forces applied by sliding ring seals.
German Patent Number DE-AS 1 226 377 discloses a sliding ring seal that is embodied as a rotating tube coupling between an electric vacuum melting furnace having a vacuum chamber. This sliding ring seal permits a wavy-type displacement, because the sealing ring has a resilient compensating component. However, this does not eliminate the aforementioned disadvantages of the prior art, i.e. high maintenance and replacement expense, resistance to abrasive substances, etc.